Lock thread die set and method

ABSTRACT

A lock thread die set and method of forming a lock thread is disclosed wherein a split crest locking thread is formed on a workpiece. First and second dies cooperate with a workpiece to roll a first thread form on the workpiece and near the end of the thread forming a lock thread form section on one die has a crest which extends from the root in a position to engage the crest of the thread being formed on the workpiece. This crest splits the forming crest into a diverging double V-shaped crest along an intermediate portion of the length of the workpiece. The above description is merely one form of the invention and is not to be construed as limiting on the scope of the invention.

United States Patent [191 Matej 1 Mar. 25, 1975 1 1 LOCK THREAD DIE SET AND METHOD [75] Inventor: Ronald ,1. Matej, Parma, Ohio [73] Assignee: Prutton Corporation, Cleveland,

Ohio

[22] Filed: June 18, 1973 [21] Appl. No.: 371,274

3,489,195 1/1970 Mortus 3,653,241 9/1972 Orlomoski 72/469 3,693,389 9/1972 Podell et a1 72/469 X 3,772,720 11/1973 Yomamoto 72/88 X Primary E.\aminerMilton S. Mehr V Attorney, Agent, or Firm-Louis V. Granger [57] ABSTRACT A lock thread die set and method of forming a lock thread is disclosed wherein a split crest locking thread is formed on a workpiece. First and second dies cooperate with a workpiece to roll a first thread form on the workpiece and near the end of the thread forming a lock thread form section on one die has a crest which extends from the root in a position to engage the crest of the thread being formed on the workpiece. This crest splits the forming crest into a diverging double V-shaped crest along an intermediate portion of the length of the workpiece. The above description is merely one form of the invention and is not to be construed as limiting on the scope of the invention.

25 Claims, 7 Drawing Figures LOCK THREAD DIE SET AND METHOD BACKGROUND OF THE INVENTION Many different forms of lock threads have been developed, including deforming the metal of the threads or adding a plastic pellet at one side of the threads. Also, cuts have been made in the flange of the thread of the workpiece to deform the regular thread shape. Also, the thread crests have been truncated or some crests have been changed in pitch angle to form a locking thread. All these prior art forms take special dies or a secondary operation on the completed workpiece in order to establish the locking thread. Accordingly, an object of the invention is to provide a locking thread on a workpiece which obviates the above mentioned disadvantages.

Another object of the invention is to form a locking thread on a workiece at the same time that the regular thread is being formed.

Another object of the invention is to provide a locking thread on a workpiece which does not require a secondary operation and does not require foreign materials on the workpiece.

Another object of the invention is to provide a locking thread on a workpiece by a die set which is easily and quickly manufactured and prepared for a thread rolling operation.

SUMMARY OF THE INVENTION The invention may be incorporated in a thread rolling die set for a machine to form a split crest locking thread on a workpiece, comprising, in combination, a first and a second die, a first thread form section and a lock thread form section on the working surface of said first die spaced in a direction transversely to the length ofthe first die, a thread form on the working surface of said second die of the same pitch and substantially the same form as said first thread form section on said first die, said dies being mountable for relative movement to cooperate with a circular cross section workpiece disposable between the working surfaces thereof for rolling a workpiece therebetween, said lock thread form section being of the same pitch as said first thread form section, and a crest extending from the root of said lock thread form toward said second die to form a split crest locking thread on a part of a workpiece.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawing, in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of a machine embodying the invention;

FIG. 2 is a perspective view of the rotary die of the die set;

FIG. 3 is an elevational view of the stationary die of the die set;

FIGS. 4, and 6 are enlarged sectional views on line 44, 55 and 6-6 of FIG. 1;

and FIG. 7 is a view similar to FIG. 5 of a modifica tron.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a machine 11 which utilizes the pre ferred die set for form rolling a split crest locking thread on a workpiece 12. The machine 11 has a frame 13 having a motor 14 to rotate a spindle 15. The spin dle 15 carries a rotary die 16 tocooperate with a stationary die 17. The rotary die 16 may be in the form of a continuous circular ring with plural starts thereon, as shown in FIG. 2. The stationary die 17 may be an arcuate shoe clamped by clamps 18 to an adjustable die holder 20. This die holder 20 is held by adjusting screws 21 on the frame 13 which adjusts the space between the dies 16, 17 at the entrance end 22 and the exit end 23 of the dies. This permits the workpieces 12 to roll in a planetary motion in the space between the dies from the entrance end to the exit end as the spindle 15 rotates clockwise, as shown in FIG. 1.

A workpiece feed chute 25 is provided to supply workpieces to the entrance end 22 and a workpiece feed finger 26 reciprocates in guides 27 by means of a bell crank 28 driven from a rotating cam 29 on the spindle 15 to feed successive workpieces to the space between the dies. Other feeding arangements may be utilized, this preferred embodiment having been found to operate quite satisfactorily to rapidly feed workpieces to the dies. The machine 11 may have a horizontal or vertical axis 31 of the spindle 15 or it may be set at an angle to the vertical.

FIG. 2 illustrates the rotary die 16 as a shell held by clamps 33 on the spindle 15. The working surface of the die 16 is the outer, generally cylindrical surface. This working surface has thereon multiple starts of a first thread form 34 of the form of the thread desired on the workpiece 12. This thread form may be any of the usual thread forms and an ordinary V-shaped thread form has been shown.

FIG. 3 is an elevational view of the working surface of the arcuate stationary die shoe 17. This die has a concave generally circular working surface as viewed in FIG. 3. This working surface has thereon a multiple start first thread form section 35, a locking thread form section 36, and a third thread form section 37. The first and third thread form sections 35 and 37 are the same in pitch and shape and would be continuous were it not for the locking thread form section 36. The locking thread form section 36 is better illustrated in FIGS. 4, 5 and 6 which show progressively the action thereof on a planetary moving workpiece 12.

FIG. 4 shows the section 36 as containing splitting means including V-shaped crests 40 extending from the root of the lock thread form toward the rotary or second die 16. The crests 40 may be interrupted, or as shown, may be continuous The root of the section 36 is flat between these crests 40 and the crests have only about one-half the height, that is, the crest-to-root dimension of the thread form on section 35 or section 37. The V-shaped crests 40 are also substantially out of phase with the crests on the sections 35-37. In other words, the crests of the locking section 36 are at those places whereat a root would be located, considering the first thread form section 35. Viewing FIG. 3, the crests of the locking thread form section 36 are in alignment with the roots of the first thread form section 35 and thus both sections 35 and 36 have the same pitch. The pitch of the thread is defined in *Machinerys" Handbook, namely, the distance from the center of one thread to the center of the next thread.

The sequence from FIG. 4 to FIG. 5 to FIG. 6 shows the progressive thread rolling action from the entrance to the exit end of the dies, although not necessarily a workpiece at each such position of FIG. 1. This shows that the locking section 36 begins at a position sufficiently recessed that the V-shaped crests 40 do not contact the workpiece. At the exit end shown in FIG. 6 the V-shaped crests 40 are positioned substantially in the same geometrical cylinder of the tip of the crests of the first and third sections and 37. This recessing of the locking section 36 at the entrance end is shown by the dotted line 41 in FIG. 1.

OPERATION The rotation of the spindle l5 and the cam actuation of the feed mechanism will feed one workpiece 12 to the entrance end 22 of the dies each 90 degrees of rotation of the rotary die 16. The locking thread form section 36 is provided on at least one die and in the preferred embodiment is shown as being on the first or stationary die 17. The FIGS. 4, 5 and 6 show the progression of the thread forming operation which also forms a locking thread 42 on a part of the workpiece 12. Near the beginning of the thread rolling operation, FIG. 4 shows that the crests of the first thread form sections 34 and 35 begins to rollingly deform the metal of the workpiece 12 into two rows as at 43. This is the beginning of the V-shaped crest on the workpiece. Near this entrance end 22 of the dies the locking thread section 36 is sufficiently recessed that it does not engage the workpiece 12. FIG. 5 illustrates the thread rolling action about one-half or two-thirds completed. The locking section 36 is positioned closer to the rotary die 16 and may begin to touch the converging rows of deformed metal 44. FIG. 6 shows the action at the exit end 23 of the dies. At this position the thread rolling action of the first thread forms 34 and 35 and the third thread form section 37 is completed. The locking section 36 is positioned to have the crests thereof at the same level as the crests of the first and third sections 35 and 37. Accordingly, only the locking section 36 of the dic 17 rollingly engages the workpiece 12. This locking section 36 then establishes that the splitting means of the V-shaped crests 40 force open the Vshaped crest of the two rows 44 forming the crest of the workpiece. In fact, the V-shaped die crests 40 keep the crest of the workpiece from closing. This establishes the diverging double V-shaped crest locking thread 42 on the workpiece. A recess 46 is provided in the rotary die 16 to prevent closing these diverging double V-shaped crests. FIG. 2 shows that the recesses 46 are rectangular and extend for about one-third the length of the thread rolling action thereof. As shown in FIG. 1, there are four possible feed points of workpieces around the periphery of the rotary die 16. Each recess 46 has a circumferential length equal to about one-third of the circumferential length of the die surface which works on a particular workpiece. Accordingly, near the exit end 23, when the locking section 36 is actively working on a workpiece, the recess 46 is provided opposite thereto on the rotary die 16 to prevent closing the newly formed diverging double V crest of the locking thread 42.

Workpicces are shown dotted in FIG. 1 to illustate the progressive rolling action of FIGS. 4, 5 and 6. These workpieces 12 are incorrectly spaced on FIG. 1, because, with four possible feed points, and due to the planetary action, they would be spaced at 45 degree intervals around the rotary die 16.

FIG. 6 shows that when the locking section 36 is working on the workpiece then the first and third sections 35 and 37 generally are not even touching the workpiece 12. FIGS. 4, 5 and 6 also illustrate that the lower end 48 of the workpiece has imperfect threads for the start of the threads and also the upper end 49 of the workpiece has imperfect threads as they merge with the cylindrical shank of the workpiece. These sections 35, 36 and 37 may be of any dimension perpendicular to the direction of thread rolling to form threads on any length of workpiece. The locking thread 42 has been shown at an intermediate portion of the workpiece 12 as a preferred embodiment but obviously may be placed anywhere along the length of workpiece 12.

FIG. 7 shows a modification with the only change being from locking thread form section 36 to a modified form 36A. This locking section 36A has an ordinary V-shaped crest and root, the same as on the first section 35. The action on the workpiece 12 is the same as in FIGS. 4, 5 and 6 because only the crests of the lock form section 36A act on the workpiece. FIG. 7 is a view similar to FIG. 5 and shows the workpiece at an intermediate stage. The finished workpiece will appear as in FIG. 6 with a diverging double V-shaped crest locking thread 42.

The die set of FIGS. 2 and 3 is exceptionally easy to make. The rotary die 16 is made by the usual method of cutting or grinding and then the recesses 46 are formed, as by milling. The stationary die 17 of FIG. 3 is made in three parts, sections 35, 36 and 37. Sections 35 and 37 may be made at one time with a spacer therebetween the same thickness as the die section 36. The first thread form is made in the usual manner on the working surface of sections 35 and 37. The locking thread form is made separately on the section 36 and it is then substituted for the spacer between sections 35 and 37. Fastening together these three sections then completes the stationary die 17.

The die set of FIG. 7, including locking section 36A, may be made in an even simpler manner. All sections 35, 36A and 37 may be made at one time. Viewing FIG. 3 the section 36A would be shifted longitudinally a distance B equal to the circumferential distance between a crest 51 and a root 52 on the finished die. This distance may be easily calculated by knowing the pitch angle and the number of threads per inch. A distance A will be the dimension, perpendicular to dimension B, between the root and crest on section 35. Then distance B will equal A/tana. After the threads are cut or ground simultaneously in all three sections 35, 36A and 37, then locking section 36A will be shifted longitudinally back to the position of FIG. 3. The entrance end of this section 36A will then be recessed so it is farther from the rotary die 16. The three sections are then fastened together to complete the stationary die 17.

In both modifications it will be noted that the crests of the locking thread form section are substantially directly out of phase with the crests of the first thread form section. The rolling action of the dies on the workpiece form nearly completely the first thread form on the workpiece before operating thereon with the locking thread form section. On the workpiece 12 as viewed in FIG. 6, the crest to root dimension of the diverging double V-shaped crest is substantially less than and approximately one-half that on the first thread form. As viewed in FIG. 3, the crest of the first die locking thread form section 36 is in alignment with the root of the first die first thread form section 35. FIG. 3, for example, shows that the first thread form section 35 and the locking section 36 are laterally spaced on the first die relative to the length thereof to operate on different portions of a workpiece. FIGS. 5 and 6 illustrate that the first thread form section 34 on the second die 16 and the locking section 36 operate successively on the same portion of the workpiece 12.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerour changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

l. A thread rolling die set for a machine to form a split crest locking thread on a workpiece, comprising, in combination,

a first and a second die,

a first thread form section and a lock thread form section on the working surface of said first die spaced in a direction transversely to the length of the first die,

a thread form on the working surface of said second die of the same pitch and substantially the same form as said first thread form section on said first die,

said dies being mountable for relative movement to cooperate with a circular cross section workpiece disposable between the working surfaces thereof for rolling a workpiece therebetween,

said lock thread form section being of the same pitch said first thread form section,

and splitting means including a crest extending from the root of said lock thread form toward said second die to keep converging rows of material of a workpiece from closing to form a split crest locking thread on a part of a workpiece.

2. A thread rolling die set as set forth in claim 1 wherein said die set includes an arcuate stationary die and a rotary die.

3. A thread rolling die set as set forth in claim 1 wherein said first die is an arcuate stationary die and said second die is a rotary shell die.

4. A thread rolling die set as set forth in claim 1 wherein said first thread form is a multiple start V- shaped thread rolling form on the working surface of said first die.

5. A thread rolling die set as set forth in claim 1 wherein said first thread form is a multiple start V- shaped thread rolling form on the working surface of each of said dies.

6. A thread rolling die set as set forth in claim 1 wherein said lock thread form section has plural crests substantially directly out of phase with the crests of said first thread form section.

7. A thread rolling die set as set forth in claim 1 in cluding plural crests in said splitting means, and a flat root between crests on said lock thread form section.

8. A thread rolling die set as set forth in claim I wherein said lock form thread on the workpiece has a crest-to-root dimension substantially one-half that on said first thread form section. V

9. A thread rolling die set as set forth in claim 1 wherein said crest of said lock thread form section has a V-shape at substantially the same included angle as that on said first thread form section.

10. A thread rolling die set as set forth in claim 1, including an entrance end and an exit end on said first die, and said lock thread form section being positioned to operate on a workpiece adjacent said exit end.

11. A thread rolling die set as set forth in claim 1 wherein said lock thread form section is approximately the length of said first die.

12. A thread rolling die set as set forth in claim 1 including an entrance end and an exit end on said first die, wherein said lock thread form section is approximately the length of said first die and progressively is positioned closer to said second die from said entrance end to said exit end.

13. A thread rolling die set as set forth in claim 1 including an entrance end and an exit end on said first die, wherein the crests of all thread forms on said sections of said first die are at substantially the same level except said lock thread form section in which the crest is recessed away from said second die progressively from said exit end to said entrance end.

14. A thread rolling die set as set forth in claim I including recess means in the working surface of said second die positioned to be opposite said lock thread form section as a workpiece is being roll formed by said lock thread form section.

15. A thread rolling die set as set forth in claim 14 wherein said second die is a rotary die and said recess means includes a plurality of rectangular recesses in the working surface of said second die at intervals spaced around the periphery of said rotary second die corresponding to the spacing between successive workpiece possible feed points.

16. A thread rolling die set as set forth in claim 1 wherein said splitting means crest of said lock thread form section has a V-shape to split the crest of the workpiece into a self-locking thread with a diverging double V-shaped crest along an intermediate portion of the length of the workpiece.

17. A thread rolling die set as set forth in claim 1, including plural crests in said splitting means, and a V- shaped root between crests of said locking thread form 7 section.

18. The method of forming a split crest locking thread on a workpiece using a first and a second die, comprising the steps of:

establishing a first thread form section and a lock thread form section on the working surface of the first die and the first thread form section on the second die,

relatively moving the dies with a circular cross section workpiece therebetween to form thereon a thread of said first thread form by progressively deforming material from the workpiece to form the root of the thread and the material being moved into two gradually converging rows to form a thread crest,

and relatively moving the dies with the workpiece therebetween to cause said lock thread form section to contact the workpiece and keep the converging rows from closing and instead to spread the rows into two diverging rows at the crest of part of the workpiece thread.

19. The method as set forth in claim 18, wherein on the workpiece the first thread form is a V-shaped crest and said lock thread form is a double V-shaped crest.

20. The method as set forth in claim 18, including forming a recess in the working surface of the second die to be disposed opposite said first die during contacting of the lock thread form section thereof with the workpiece, to thus avoid reclosing the diverging rows.

21. The method as set forth in claim 18, including forming nearly completely the first thread form on the workpiece before operating thereon with the lock thread form section.

22. The method as set forth in claim 18, wherein on j the workpiece said lock form thread is formed with a crest-to-root dimension which is substantially less than that on said first thread form.

23. The method as set forth in claim 18, including establishing the crest of the first die lock thread form section in alignment with the root of the first die first thread form section.

24. The method as set forth in claim 18, including establishing said first thread form section and said lock thread form section laterally spaced on the first die relative to the length thereof to operate on different portiohs of a workpiece.

25. The method as set forth in claim 18, including establishing said first thread-form section on the second die and said lock thread form section on the first die to operate successively on the same portion of a workpiece. 

1. A thread rolling die set for a machine to form a split crest locking thread on a workpiece, comprising, in combination, a first and a second die, a first thread form section and a lock thread form section on the working surface of said first die spaced in a direction transVersely to the length of the first die, a thread form on the working surface of said second die of the same pitch and substantially the same form as said first thread form section on said first die, said dies being mountable for relative movement to cooperate with a circular cross section workpiece disposable between the working surfaces thereof for rolling a workpiece therebetween, said lock thread form section being of the same pitch as said first thread form section, and splitting means including a crest extending from the root of said lock thread form toward said second die to keep converging rows of material of a workpiece from closing to form a split crest locking thread on a part of a workpiece.
 2. A thread rolling die set as set forth in claim 1 wherein said die set includes an arcuate stationary die and a rotary die.
 3. A thread rolling die set as set forth in claim 1 wherein said first die is an arcuate stationary die and said second die is a rotary shell die.
 4. A thread rolling die set as set forth in claim 1 wherein said first thread form is a multiple start V-shaped thread rolling form on the working surface of said first die.
 5. A thread rolling die set as set forth in claim 1 wherein said first thread form is a multiple start V-shaped thread rolling form on the working surface of each of said dies.
 6. A thread rolling die set as set forth in claim 1 wherein said lock thread form section has plural crests substantially directly out of phase with the crests of said first thread form section.
 7. A thread rolling die set as set forth in claim 1 including plural crests in said splitting means, and a flat root between crests on said lock thread form section.
 8. A thread rolling die set as set forth in claim 1 wherein said lock form thread on the workpiece has a crest-to-root dimension substantially one-half that on said first thread form section.
 9. A thread rolling die set as set forth in claim 1 wherein said crest of said lock thread form section has a V-shape at substantially the same included angle as that on said first thread form section.
 10. A thread rolling die set as set forth in claim 1, including an entrance end and an exit end on said first die, and said lock thread form section being positioned to operate on a workpiece adjacent said exit end.
 11. A thread rolling die set as set forth in claim 1 wherein said lock thread form section is approximately the length of said first die.
 12. A thread rolling die set as set forth in claim 1 including an entrance end and an exit end on said first die, wherein said lock thread form section is approximately the length of said first die and progressively is positioned closer to said second die from said entrance end to said exit end.
 13. A thread rolling die set as set forth in claim 1 including an entrance end and an exit end on said first die, wherein the crests of all thread forms on said sections of said first die are at substantially the same level except said lock thread form section in which the crest is recessed away from said second die progressively from said exit end to said entrance end.
 14. A thread rolling die set as set forth in claim 1 including recess means in the working surface of said second die positioned to be opposite said lock thread form section as a workpiece is being roll formed by said lock thread form section.
 15. A thread rolling die set as set forth in claim 14 wherein said second die is a rotary die and said recess means includes a plurality of rectangular recesses in the working surface of said second die at intervals spaced around the periphery of said rotary second die corresponding to the spacing between successive workpiece possible feed points.
 16. A thread rolling die set as set forth in claim 1 wherein said splitting means crest of said lock thread form section has a V-shape to split the crest of the workpiece into a self-locking thread with a diverging double V-shaped crest along an intermediate portion of the length of the workpiece.
 17. A thread rolling die set as set forth in claim 1, including plural crests in said splitting means, and a V-shaped root between crests of said locking thread form section.
 18. The method of forming a split crest locking thread on a workpiece using a first and a second die, comprising the steps of: establishing a first thread form section and a lock thread form section on the working surface of the first die and the first thread form section on the second die, relatively moving the dies with a circular cross-section workpiece therebetween to form thereon a thread of said first thread form by progressively deforming material from the workpiece to form the root of the thread and the material being moved into two gradually converging rows to form a thread crest, and relatively moving the dies with the workpiece therebetween to cause said lock thread form section to contact the workpiece and keep the converging rows from closing and instead to spread the rows into two diverging rows at the crest of part of the workpiece thread.
 19. The method as set forth in claim 18, wherein on the workpiece the first thread form is a V-shaped crest and said lock thread form is a double V-shaped crest.
 20. The method as set forth in claim 18, including forming a recess in the working surface of the second die to be disposed opposite said first die during contacting of the lock thread form section thereof with the workpiece, to thus avoid reclosing the diverging rows.
 21. The method as set forth in claim 18, including forming nearly completely the first thread form on the workpiece before operating thereon with the lock thread form section.
 22. The method as set forth in claim 18, wherein on the workpiece said lock form thread is formed with a crest-to-root dimension which is substantially less than that on said first thread form.
 23. The method as set forth in claim 18, including establishing the crest of the first die lock thread form section in alignment with the root of the first die first thread form section.
 24. The method as set forth in claim 18, including establishing said first thread form section and said lock thread form section laterally spaced on the first die relative to the length thereof to operate on different portions of a workpiece.
 25. The method as set forth in claim 18, including establishing said first thread form section on the second die and said lock thread form section on the first die to operate successively on the same portion of a workpiece. 